[lldb-dap] Addressing the order of events during disconnect to flush output. (#128583)

The TestDAP_ouput test is flaky due to the order of events during
shutdown. We were stopping the output and error handle redirection after
we finished the disconnect request, which can cause us to miss output
events due to timing. Moving when we stop the redirection to ensure we
have consistent output prior to disconnect responding.

Fixes #128567

Author: ashgti

lldb/test/API/tools/lldb-dap/output/TestDAP_output.py

@@ -16,6 +16,7 @@ def test_output(self):
         program = self.getBuildArtifact("a.out")
         self.build_and_launch(
             program,
+            disconnectAutomatically=False,
             exitCommands=[
                 # Ensure that output produced by lldb itself is not consumed by the OutputRedirector.
                 "?script print('out\\0\\0', end='\\r\\n', file=sys.stdout)",
@@ -33,6 +34,9 @@ def test_output(self):
 
         self.continue_to_exit()
 
+        # Disconnecting from the server to ensure any pending IO is flushed.
+        self.dap_server.request_disconnect()
+
         output += self.get_stdout(timeout=lldbdap_testcase.DAPTestCaseBase.timeoutval)
         self.assertTrue(output and len(output) > 0, "expect program stdout")
         self.assertIn(

lldb/tools/lldb-dap/DAP.cpp

@@ -223,10 +223,7 @@ llvm::Error DAP::ConfigureIO(std::FILE *overrideOut, std::FILE *overrideErr) {
   return llvm::Error::success();
 }
 
-void DAP::StopIO() {
-  out.Stop();
-  err.Stop();
-
+void DAP::StopEventHandlers() {
   if (event_thread.joinable()) {
     broadcaster.BroadcastEventByType(eBroadcastBitStopEventThread);
     event_thread.join();
@@ -853,13 +850,17 @@ lldb::SBError DAP::Disconnect(bool terminateDebuggee) {
 
   SendTerminatedEvent();
 
+  // Stop forwarding the debugger output and error handles.
+  out.Stop();
+  err.Stop();
+
   disconnecting = true;
 
   return error;
 }
 
 llvm::Error DAP::Loop() {
-  auto stop_io = llvm::make_scope_exit([this]() { StopIO(); });
+  auto cleanup = llvm::make_scope_exit([this]() { StopEventHandlers(); });
   while (!disconnecting) {
     llvm::json::Object object;
     lldb_dap::PacketStatus status = GetNextObject(object);

lldb/tools/lldb-dap/DAP.h

@@ -228,8 +228,8 @@ struct DAP {
   llvm::Error ConfigureIO(std::FILE *overrideOut = nullptr,
                           std::FILE *overrideErr = nullptr);
 
-  /// Stop the redirected IO threads and associated pipes.
-  void StopIO();
+  /// Stop event handler threads.
+  void StopEventHandlers();
 
   // Serialize the JSON value into a string and send the JSON packet to
   // the "out" stream.